Diminished Guitar Chords in Theory & Practice

This lesson
will explain the theory behind diminished guitar
chords and their function.

There's a lot of confusion around how diminished chords work in
music. I often get asked the question of "when to use them" in a chord
progression.

As with music in general, there are no hard and fast rules
(except "if it sounds good, play it!"),
but I'll take you through some of the tried and tested functions
diminished chords can
serve in your music.

Even if you were just looking for a chord
chart (which is further down the page), read through the whole lesson,
split over a few days,
as it will prove very rewarding as far
as developing your improvisation and songwriting skills.

Diminished chord theory - how to construct them

Diminished chords ("diminished" referring to the diminished
5th in the chord) have an
unstable sound. They create an air of tension and unresolve (hear the
examples below) which is what makes them wonderfully intriguing chords
to use in
your music.

There
are 3 main types of diminished chord, as shown in the table below.

Note that if you see
the ° symbol
after the chord letter (e.g. C°), it means "diminished". When
typing, some
people just use "o" as the proper symbol requires digging out the
character map!

As you can see, there's a common occurence of the root
(1), b3 (flat/minor 3rd)
and b5
(flat 5th) in the three types. These are the most important tones in
any diminished chord or scale. The flat 5th in relation to a minor 3rd
is what gives it that unstable quality.

So, a diminished triad
can simply be thought of as a minor
chord with a flat
5th.

A half diminished
chord is the above diminished
triad
with an added flat 7th.
This chord is also sometimes written as m7b5 (minor 7 flat
5) e.g. Cm7b5.

A diminished seventh
chord is a diminished
triad with an added diminished
7th.
That's another way of saying "double flat 7th". So the only difference
between a dim7 and m7b5 chord is the 7th is flattened another semitone
in dim7 chords.

First, just make clear in your mind these
distinctions as each one has a different sound and function which we'll
look at shortly.

Diminished guitar chords chart - how to play them

To
help you
play along throughout this lesson, here are the most common
diminished guitar chord forms used in chord progressions with their
fingerings.

Note
that I haven't included diminished triads, because these are most
commonly extended to half diminished or diminished 7th. You can see how
the triad exists in both these types.

Half diminished chord chart

E
string shapes

A
string shape
D string
shape

Diminished seventh chord chart

E
string shapes

A
string shape
D string
shape

Diminished chords function - when to use them

As mentioned earlier, occurences of the diminished triad
are often extended to half diminished or diminished 7th chords,
because they sound more... interesting. Essentially, you're playing the
diminished triad in both those variations anyway, so they're just a
meatier, more colourful version of the triad.

So, whenever there is an occurence of a diminished chord then you
should try both m7b5
(half diminished) or dim7
and go with the one that sounds best to you.

Let's look at some typical uses of the chord.

Leading tone (vii)
diminished chord

In
major keys,
a half diminished chord naturally occurs on the 7th degree
(called the leading tone or vii).
In plain English that means whatever the
major tonic (I)
chord is, the diminished chord naturally sits one
semitone/fret
down from that.

It's called a "leading tone" or "leading chord"
because it naturally resolves or "leads" to the tonic. You can hear an
example here. See the table
below for a breakdown...

Key
/ Tonic Chord

Lead
tone
chord

Examples

C major

Bdim

F / Bdim / C
Dm / Bdim / C
Am / Bdim / C

C# major

Cdim

F# / Cdim / C#
Ebm / Cdim / C#
Bbm / Cdim / C#

D major

C#dim

G /
C#dim / D
Em / C#dim / D
Bm / C#dim / D

That's
just a few examples. You should be able to see this same leading tone
chord - tonic relationship no matter what key you're in.

In minor keys,
and especially minor keys based around harmonic minor, a
diminished 7th chord is the natural leading tone chord (click to hear
example).

Key
/ Tonic
Chord

Lead
tone
chord

Examples

C minor

Bdim7

F / Bdim7 / Cm

C# minor

Cdim7

F# / Cdim7 /
C#m

D minor

C#dim7

G /
C#dim7 / Dm

Half diminished iii
chord

In major key progressions, the iii
chord (naturally minor) is sometimes replaced with a half
diminished iii.
You'll hear this most commonly used in jazz. For
example...